1. Field of the Invention
The present invention relates to a wheelbarrow such as a manual-push type single-wheeled carrier and, more particularly, to a power-assisted wheelbarrow having an electric motor for assisting with moving the wheelbarrow.
2. Related Art
A wheelbarrow such as a manual-push single-wheeled carrier can easily pass through a narrow road and is widely used for carrying materials, parts, harvests or fertilizers at jobsites, in fields, fruit farms, mountains or forests. Since the carrier is pushed manually, however, it requires heavy manual labor on roads covered with pebbles or bricks or on slopes of severe gradients, so that the range of its application is restricted.
As disclosed in Japanese Utility Model Laid-Open Nos. 3-100568 and 7-40354, therefore, carriers are disclosed in which manual labor is reduced by giving the wheel an assisting force of an electric motor activated by electric power supplied from a battery.
In the carriers disclosed in Japanese Utility Model Laid-Open Nos. 3-100568 and 7-40354, a constant assisting force is applied from an electric motor to the wheel by turning on a switch which is mounted on the rear end portion of the handles of the manual-push carrier. At this time, the constant assisting force has to be set to a relatively high level so as to avoid providing an assisting force which is too low. If the movement by the assisting force is continued, the electric motor generates a larger assisting force than necessary so that the battery is inconveniently depleted early. If the capacity of the battery is increased, an increase in the weight of the carrier causes an operation problem because the function of the wheelbarrow is deteriorated.